Comparative life cycle GHG emissions from local electricity generation using heavy oil, natural gas, and MSW incineration in Macau
Introduction
At present, one of the ongoing challenges facing human society is to continue providing electricity energy in usable forms while fossil fuel reserves are declining, populations are growing, and concerns about global warming are increasing. From 1973–2013, world gross electricity production increased from 6144 TW h to 23,391 TW h, with an average annual growth rate of 3.4% [1]. Electricity consumption is now responsible for a large share (about 40%) of global greenhouse gas (GHG) emissions, and 67.2% of world electricity production in 2013 was from fossil fuel-powered plants, making them the key players for developing GHG mitigation strategies for the energy sectors and electricity production sectors [2], [3], [4]. The future electricity production mix and associated environmental challenges has been a focus of debate among policy makers, related experts, and the general public in recent years [5]. The demand for a green power grid has become urgent, internationally.
The increased awareness of the importance of environmental protection in our society and the growing concern over future sources of electricity generation have led to inquiries as to how much environmental impact is caused in producing the electricity. Any decisions to be taken also require a clear understanding of the potential environmental impacts of electricity produced by existing technologies. However, previous studies have focused on the direct emissions of power plants, and considered only emissions caused by burning fossil fuels. Instead, consideration should be extended to account for indirect emissions, including upstream materials and energy mining and processing [6], [7]. Life Cycle Assessment (LCA) is a widely accepted approach to handling such environmental analysis of a product or a system from “cradle to grave” [8], [9]. LCA can reveal the importance of “hidden” processes and materials pertaining to an individual product or component. This in turn gives an indication of the environmental impact of each technology in terms of its contribution to environmental effects such as climate change [10], [11], [12], [13]. The comprehensive scope of LCA is useful in avoiding problem-shifting from one life cycle phase to another, from one region to another, or from one environmental problem to another [14]. In the particular case of electricity production, a number of different technologies have been widely assessed. Some LCA studies have compared renewable and fossil fuels as well as nuclear energy in the same or different countries or regions [15], [16], [17], [18], [19], [20], [21], [22], [23].
Electricity is an essential energy carrier in modern society, and the emission data related to electricity generation are used extensively for accounting and reporting purposes. Electricity usage and its associated primary energy consumption and emissions are important contributors to the life cycle impacts of many products and systems, as well as to GHG inventories of entities, products, and countries [24], [25], [26]. Actually, these datasets and emission factors for electricity generation (e.g., kg CO2 eq/kW h) have been used often when performing LCA and/or GHG emission accounting of the products or the system in many studies [11]. Due to the differences of energy sources, the actual electricity generation processes and the management levels, there are large gaps among life cycle inventory (LCI) datasets for similar electricity technologies in different countries or regions. Edenhofer et al. [27] attributed these differences to technology characteristics, local conditions and LCA methodological aspects. LCI databases, such as Ecoinvents and GaBi Database [28], [29], provide information for a large number of processes but are at the same time far from complete, especially for the other countries and regions except the EU countries [9], [10]. Approximations and assumptions are often made if appropriate data are not readily available, which could bring the large influences on the representative of the research results. Therefore, considering the importance of data reliability, despite the large number of studies and the commercial database, more research that assess the regional electricity generation are still needed.
Macau, a Special Administrative Region (SAR) of China, is an autonomous territory on the western side of the Pearl River Delta, China. The population of Macau, which covers only 30.4 km2, has risen from 0.43 million in 2000 to 0.65 million people in 2015—a 49% increase, and the population is expected to continue to grow for the next decade or more [30]. The GDP of Macau has been growing by roughly 13.6% per year from 2000 (15,659 U.S. dollars) to 2014 (89,267 U.S. dollars). In 2015, the total electricity consumption in Macau was 4.97 billion kW h (approximately 7700 kW h/capita·year), about 3 times the world's average annual electricity consumption of 2594 kW h/capita in 2010 [2], [30]. Because a huge amount of electricity is imported from mainland China (Fig. S1), the local power plants generated only 753 million kW h in 2015. Most of the local electricity is generated from three energy sources: heavy oil, natural gas, and municipal solid waste (MSW) incineration. Unlike most other countries and regions, Macau's geographically small size severely limits the number of locations where power plants can be sited, and consequently most the electricity generation plants in Macau are located very close to residential areas, causing a large potential environmental risk to local residents. Furthermore, because there are few industrial facilities in Macau, electricity generation plants are the primary stationary sources emitting pollutants into the air. Indeed, after transportation-sector emissions, local electricity generation has become the main source of GHG emissions in Macau [31].
The GHG emissions performance of electricity generation in Macau was calculated by conducting an LCA study based on the international standards of the ISO 14040 series [8], [32]. The goal of this study was to establish a scientific baseline that evaluates and compares the GHG emissions of three electricity sources in Macau. In order to quantify the GHG emissions from the current electricity grid, and to help making appropriate decisions to achieve GHG reductions in Macau, this study will: (i) estimate the GHG emissions of each of the three local electricity-generation sources in Macau, using an LCA approach; (ii) compare the results to other technologies and other countries; (iii) discuss potential GHG emission reduction strategies, using scenario analysis; and (iv) finally perform sensitivity analysis on the primary influence factors. We think such an understanding of the GHG emissions of current electricity grid could help decision makers about GHG emissions mitigation in Macau. The datasets and emission factors for electricity generation in Macau obtained in this work can be used as the basic data or the references for evaluating the potential environmental effects of other products or systems in Macau or neighborhood, and can also enrich the current commercial LCI databases.
Section snippets
Electricity generation in Macau
In Macau, the local electricity generation mainly comes from two sources: Macau power plants (CEM) and Macau Incineration plant (MIP). Actually, the CEM consists of three power stations located respectively in the Macau City namely Macau Power Station (CMC) and two on the Coloane Island namely Coloane A Power Station (CCA) and Coloane B Power Station (CCB). The details about the electricity generation in Macau are shown as follows.
- (1)
Oil-fired power station: Though most of oil is used for
Oil-fired power station (CCA)
The LCA results of the GHG emissions of the CCA during 2010–2014 are shown in Table 4. The results show that the GHG emissions per kW h varied from 0.68 to 0.75 kg CO2 eq in 2010–2014; the mean value was 0.71 kg CO2 eq. According to the LCA results, the direct GHG emissions of CCA (0.56–0.61 kg CO2 eq/kW h) contributed more than the indirect emissions, accounting for a mean of 81.04% (min.80.49% and max. 81.49%) of the total GHG emissions in 2010–2014. In Macau, most of the materials and fossil fuel
Outlook and policy recommendations
The electricity generation processes represent a large contribution to the potential GHG emissions in Macau. In this study, the GHG emissions from the local electricity generation were estimated through a LCA process and compared with other traditional energy modes and clean energy. Results show that the mean GHG emissions of electricity from heavy oil, natural gas, and MSW incineration are 0.71, 0.42, 0.95 kg CO2 eq /kW h, respectively. All the direct GHG emissions of the three electricity
Acknowledgments
This work was supported by the Foundation for Development of Science and Technology of Macau (No. 083/2015/A3), the Shenzhen Science and Technology Plan (No. JCYJ20150525092941042) and the Young Faculty Promotion Plan of Guangdong Province (YQ2015139). We also acknowledge the editor and anonymous reviewers for the valuable comments and suggestions.
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